(319b) Flow Patterns in a Dual Square Bubble Column with Uneven Aeration and Liquid Co-Flow

Experimental investigations were performed on the mutual interaction of two parallel square bubbly streams, each comprising bubbles of essentially uniform size and being assisted by liquid co-flow. We used Bubble Image Velocimetry to capture global flow patterns. In addition, dual-tip optical fibre probes were used to measure local void fractions, bubble velocities and chord lengths at two positions in the dual column. Depending on the degree of uneven gas sparging and depending on whether the liquid co-flow was uniform or also a-symmetric, we observed various flow patterns. It was possible to compensate differences in aeration rate by differences in liquid co-flow such that no buoyancy driven flow structures emerged. In this case, the bubbles move essentially rectilinear and a mixing layer pattern was visible. For all other cases, when the gas fractions left and right were not equal, the bubbly flow with the highest gas fraction always accelerated as a result of buoyancy differences and triggered large-scale flow instabilities. In general, we found a mitigating effect of liquid co-flow on such flow instabilities. Under certain conditions, we observed buoyancy driven vortex roll-up structures.